Due to rod-like hydroxyapatite crystal organizations, dental enamel is optically anisotropic, i.e... more Due to rod-like hydroxyapatite crystal organizations, dental enamel is optically anisotropic, i.e., birefringent. Healthy enamel is known to be intrinsically negatively birefringent. However, when demineralization of enamel occurs, a considerable number of inter-crystallite spaces would be created between the crystallites in the enamel, which could lead to a sign reversion in birefringence of the enamel structure. We propose that this sign reversion can be leveraged in polarization sensitive OCT (PSOCT) imaging to differentiate early caries lesions from healthy enamel. In this study using PSOCT, we first confirm that the change in birefringence sign (negative to positive) can lead to a 90-degree alteration in the local axis orientation because of the switch between the fast and slow optic axes. We then demonstrate, for the first time, that the local axis orientation can be utilized to map and visualize the WSLs from the healthy enamel with a unique contrast. Moreover, the sharp alte...
Various manipulations on JPEG images introduce single and multiple compression artifacts for forg... more Various manipulations on JPEG images introduce single and multiple compression artifacts for forged and unmodified areas respectively. Based on the statistical analysis of JPEG compression cycle and on the finite mixture paradigm, we propose in this paper a modeling framework for AC DCT coefficients of such tampered JPEG images. Its accuracy is numerically assessed using the Kullback-Leibler divergence on the basis of a tampered JPEG image dataset built from six well-known uncompressed color image databases. To illustrate the framework utility, an application in image forgery localization is proposed. By formulating the localization as a clustering problem, we use the plug-in Bayes rule combined with a simple EM algorithm to distinguish between forged and unmodified areas. Numerous experiments show that, when the quality factor of final JPEG compression is high enough, the proposed modeling framework yields higher localization performances in terms of F 1-score than prior art regardless of divers local manipulations. INDEX TERMS DCT coefficients analysis, EM algorithm, forgery localization, multiple JPEG compression, statistical image models, tampered JPEG images.
There remains a clinical need for an accurate and non-invasive imaging tool for intraoral evaluat... more There remains a clinical need for an accurate and non-invasive imaging tool for intraoral evaluation of dental conditions. Optical coherence tomography (OCT) is a potential candidate to meet this need, but the design of current OCT systems limits their utility in the intraoral examinations. The inclusion of light-induced autofluorescence (LIAF) can expedite the image collection process and provides a large field of view for viewing the condition of oral tissues. This study describes a novel LIAF-OCT system equipped with a handheld probe designed for intraoral examination of microstructural (via OCT) and microvascular information (via OCT angiography, OCTA). The handheld probe is optimized for use in clinical studies, maintaining the ability to detect and image changes in the condition of oral tissue (e.g., hard tissue damage, presence of dental restorations, plaque, and tooth stains). The real-time LIAF provides guidance for OCT imaging to achieve a field of view of approximately 6....
The formability of the drawn part in the deep drawing process depends not only on the material pr... more The formability of the drawn part in the deep drawing process depends not only on the material properties, but also on the equipment used, metal flow control and tool parameters. The most common defects can be the thickening, stretching and splitting. However, the optimization of tools including the die and punch parameters leads to a reduction of the defects and improves the quality of the products. In this paper, the formability of the camera cover by aluminum alloy A1050 in the deep drawing process was examined relating to the tool geometry parameters based on numerical and experimental analyses. The results showed that the thickness was the smallest and the stress was the highest at one of the bottom corners where the biaxial stretching was the predominant mode of deformation. The problems of the thickening at the flange area, the stretching at the side wall and the splitting at the bottom corners could be prevented when the tool parameters were optimized that related to the thi...
2018 IEEE International Symposium on Signal Processing and Information Technology (ISSPIT), 2018
Resampling is a common manipulation in creating tampered digital images. The goal of this paper i... more Resampling is a common manipulation in creating tampered digital images. The goal of this paper is to develop an efficient detector to distinguish between a resampled TIFF image from an original TIFF image. To this end, we first propose a statistical model for resampled TIFF images by analyzing the complete processing process from a RAW image to a resampled TIFF image. Next, we formulate the detection problem as a likelihood ratio test between the models of original and resampled TIFF images. The test power is analytically evaluated in the context that all model parameters of original TIFF images are unknown. Numerous numerical experiments justify the performances of the detector.
This paper report the development of non-invasive multi-functional imaging system for dental appl... more This paper report the development of non-invasive multi-functional imaging system for dental applications. This system is capable of detecting: 1) autofluorescence of the enamel, 2) red porphyrin of plaque, 3) the 3D-tomography of the hard/soft tissues and 4) functional angiography of said 3D-tomography data. The imaging technique incorporates molecular imaging (via light-induced autofluorescence, or LAF), 3D-high-resolution structure (via optical coherence tomography, or OCT) and angiography (via functional OCT, or OCTA) into one single imaging probe and platform. This development is crucial for our future research that would look into possible links between our OCTA findings and other clinical indicator such as red-porphyrin of plaque, autofluorescence of enamel.
While consensus exists regarding the association between organizational commitment and job satisf... more While consensus exists regarding the association between organizational commitment and job satisfaction, the temporal ordering of this association in proposed models frequently varies across empiri...
Gingivitis is highly prevalent in adults, and if left untreated, can progress to periodontitis. I... more Gingivitis is highly prevalent in adults, and if left untreated, can progress to periodontitis. In this article, we present an interesting case study where the resolution of gingivitis was followed over a period of 10 days using optical coherence tomography (OCT) and light‐induced autofluorescence (LIAF). We demonstrate that OCT and its functional angiography can distinctively capture the changes during the resolution of gingivitis; while LIAF can detect red‐fluorescent signals associated with mature plaque present at the inflamed site. The acute inflammatory region showed evidence of angiogenesis based on the quantification of vessel density and number; while no angiogenesis was detected within the less inflamed region. Gingival thickness showed a reduction of 140 ± 26 μm on average, measured between the peak gingivitis event and the period wherein the inflammation was resolved. Vessels in the angiogenesis site was found to reduce exponentially. The mildly inflamed site showed a decreasing trend in the vessel size, which however was within the error of the measurement.
The change in gingival tissue volume may be used to indicate changes in gingival inflammation, wh... more The change in gingival tissue volume may be used to indicate changes in gingival inflammation, which may be useful for the clinical assessment of gingival health. Properly quantifying gingival tissue volume requires a robust technique for accurate registration and segmentation of longitudinally captured 3-dimensional (3D) images. In this paper, a semi-automated registration and segmentation method for micrometer resolution measurement of gingival-tissue volume is proposed for 3D optical coherence tomography (OCT) imaging. For quantification, relative changes in gingiva tissue volume are measured based on changes in the gingiva surface height using the tooth surface as a reference. This report conducted repeatability tests on this method drawn from repeated scans in one patient, indicating an error of the point cloud registration method for oral OCT imaging is 63.08 ± 4.52µm (1σ), and the measurement error of the gingival tissue average thickness is -3.40 ± 21.85µm (1σ).
We report the development of an integrated multi-functional imaging system capable of providing a... more We report the development of an integrated multi-functional imaging system capable of providing anatomical (optical coherence tomography, OCT), functional (OCT angiography, OCTA) and molecular imaging (light-induced autofluorescence, LIAF) for in vivo dental applications. Blue excitation light (405 nm) was used for LIAF imaging, while the OCT was powered by a 1310 nm swept laser source. A red-green-blue (RGB) digital camera, with a 450nm cut-on broad-band optical filter, was used for LIAF detection. The exciting light source and camera were integrated directly with the OCT scanning probe. The integrated system used two non-invasive imaging modalities to improve the speed of in-vivo OCT data collection and to better target the regions of interest. The newly designed system maintained the ability to detect differences between healthy and hypo-mineralized teeth, identify dental biofilm and visualize the microvasculature of gingival tissue. The development of the integrated OCT-LIAF system provides an opportunity to conduct clinical studies more efficiently, examining changes in oral conditions over time.
We investigate the impact of stock market cycles on unlisted firms' investment activities. We... more We investigate the impact of stock market cycles on unlisted firms' investment activities. We find that bull markets is associated with increased capital expenditures, new establishments, and employment growth in the unlisted corporate sector, while bear markets is associated with a decrease in these investment activities. The favorable effect takes one year to materialize while the adverse effect takes place contemporaneously. Both effects are transitory and vanish after two years. The effects are stronger for unlisted firms with high capital requirements and facilitated in areas with a dense presence of listed firms. In addition, the magnitude of the effect is attenuated depending on the availability of alternative financing sources such as private equity and bank lending. We also find evidence suggesting stock market cycles partly impact the unlisted firm market through merger and acquisition activities by publicly listed firms.
This paper focuses on the digital image authentication and forgery localization using demosaicing... more This paper focuses on the digital image authentication and forgery localization using demosaicing artifacts. The aim is to build an algorithm allowing a bridge between the color filter array pattern and demosaicing algorithm estimation, and the statistical analysis of demosaicing artifacts in spatial domain to improve the authentication and localization performance. After analyzing the evolution of demosaicing traces in camera acquisition pipeline, a robust feature statistic characterizing demosaiced digital images is first developed on the basis of the noise residue of green channel. Such a feature statistic is less sensitive to the edges problem because only the smooth region of green channel is used in the development. Next, a single normal mixture model is proposed to describe the probability distribution of feature statistics for both original and tampered images. Therefore, normality tests can be used to authenticate automatically digital images. The authentication performance can be further improved by human interpretation of supported graphic tools. Finally, a penalized expectation-maximization algorithm is used to localize forged areas in tampered images. Numerous comparative studies on four well-known datasets show that the developed algorithm yields better performance and robustness than existing forensics algorithms of the same kind. INDEX TERMS Demosaicing traces, digital image authentication, forgery localization, normal mixture model, penalized expectation-maximization algorithm. NHAN LE received the Engineering degree in industrial engineering and management from the
Responding to calls for studies to examine the cross-level influence of team personality composit... more Responding to calls for studies to examine the cross-level influence of team personality composition, we hypothesized a crosslevel mediation model of the effects of different operationalizations of team conscientiousness (i.e., mean, minimum, maximum, and variance) on individual safety performance through team safety climate. We tested our model using a three-wave longitudinal design with a sample of 451 employees and 70 supervisors nested within 70 teams from two branches of one hospital. The results of our multilevel path analyses indicated that the mean, minimum, and variance-but not maximum-operationalizations of team conscientiousness at time 1 were significantly related to team safety climate at time 2. Further, team conscientiousness (i.e., mean, minimum, and variance) at time 1 exerted a top-down influence on both self-ratings and supervisor ratings of individual safety compliance and safety participation at time 3 through team safety climate at time 2, suggesting that team personality composition can influence outcomes at different levels of analyses. Theoretical and practical implications of these findings are discussed.
Quantitative imaging in medicine and surgery, 2017
Recent development of optical micro-angiography (OMAG) utilizes principal component analysis (PCA... more Recent development of optical micro-angiography (OMAG) utilizes principal component analysis (PCA), where linear-regression filter is employed to separate static and blood flow signals within optical coherence tomography (OCT). While PCA is relatively simple and computationally efficient, the technique is sensitive to and easily skewed by outliers. In this paper, robust PCA (RPCA) is thus introduced to tackle this issue in traditional PCA. We first provide brief theoretical background of PCA and RPCA in the context of OMAG where coherent (complex) OCT signals are utilized to contrast blood flow. We then compare PCA and RPCA on sets of 4D-OCT complex data (3 dimensions in space and 1 dimension in time), which are collected from microfluidic phantoms andnail-fold tissue. In phantom experiments, both analyses perform relatively well since there are little motion within our observation time window, albeit small tail-noise artifacts from PCA. In nail-fold experiment, PCA suffers from tis...
Elastography has the ability of quantitatively evaluating the mechanical properties of soft tissu... more Elastography has the ability of quantitatively evaluating the mechanical properties of soft tissue, thus is helpful for diagnosis and treatment monitoring for many diseases, e.g. skin diseases. Surface acoustic waves (SAWs) have been proven to be a non-invasive, non-destructive method for accurate characterization of tissue elastic properties. Current surface acoustic wave elastography using high energy laser pulse or mechanical shaker still have some problems. In order to improve SAW elastography in medical application, a new technique was proposed in this paper, which combines high intensity focused ultrasound (HIFU) as a SAWs impulse inducer and PhS-OCT as a SAWs detector. 2% agar-agar phantom and ex-vivo porcine skin were tested. The data were processed by a new algorithm based on the Fourier analysis. The results show that the proposed method has the capability of quantifying the elastic properties of soft tissue mimicking materials. The lateral resolution of the elastogram has...
Numerical simulation of high intensity focused ultrasound temperature distribution for transcrani... more Numerical simulation of high intensity focused ultrasound temperature distribution for transcranial brain therapy AIP Conference Proceedings 1816, 080007 (2017);
2016 3rd International Conference on Green Technology and Sustainable Development (GTSD), 2016
The camera cover is a complex 3D-part with many corners and is difficult to form in deep drawing ... more The camera cover is a complex 3D-part with many corners and is difficult to form in deep drawing process. One of the most common defects is the tearing that occurs at corners due to the tensile stress concentration. The suitable determination of die and punch parameters leads to reduce the defects and improve the quality of drawn part. Both numerical and experimental analysis can be useful to analyze the deep drawing process for determining the optimal values of tool parameters. In this paper, the formability of camera cover in deep drawing process was considered relating to the geometrical parameters of the die edge radius (RD), the pocket radius on bottom of die (RD1) and the punch nose radius (RP). The results showed that the thickening occurred in the flange area, the stretching occurred in the side wall and the tearing could be occurred in the corners above the punch nose that related to stress concentration if the tool parameters were not optimized. Also, the numerical and experimental results were a good agreement. Both numerical and experimental results cleared that the quality of camera cover relating the thickness was improved when the die geometric parameters were determined suitably with values of RD = 8 mm, RD1 = 4 mm and RP = 2 mm.
International journal of hyperthermia : the official journal of European Society for Hyperthermic Oncology, North American Hyperthermia Group, Sep 5, 2016
Phase-sensitive optical coherence tomography (PhS-OCT) is proposed, as a new high intensity focus... more Phase-sensitive optical coherence tomography (PhS-OCT) is proposed, as a new high intensity focused ultrasound (HIFU) imaging guidance to detect and track HIFU focus inside 1% agar samples in this work. The experiments studied the effect of varying HIFU power on the induction of shear wave, which can be implemented as a new technique to monitor focused ultrasound surgery (FUS). A miniature HIFU transducer (1.02 MHz, 20 mm aperture diameter, 15 mm radius of curvature) was produced in-house, pressure-field mapped, and calibrated. The transducer was then embedded inside a 1% agar phantom, which was placed under PhS-OCT for observation, under various HIFU power settings (acoustic power, and number of cycles per pulse). Shear wave was induced on the sample surface by HIFU and was captured in full under PhS-OCT. The lowest HIFU acoustic power output for the detection of shear wave was found to be 0.36 W (1.02 MHz, 100 cycles/pulse), or with the number of cycles/pulse as low as 20 (1.02 MH...
Due to rod-like hydroxyapatite crystal organizations, dental enamel is optically anisotropic, i.e... more Due to rod-like hydroxyapatite crystal organizations, dental enamel is optically anisotropic, i.e., birefringent. Healthy enamel is known to be intrinsically negatively birefringent. However, when demineralization of enamel occurs, a considerable number of inter-crystallite spaces would be created between the crystallites in the enamel, which could lead to a sign reversion in birefringence of the enamel structure. We propose that this sign reversion can be leveraged in polarization sensitive OCT (PSOCT) imaging to differentiate early caries lesions from healthy enamel. In this study using PSOCT, we first confirm that the change in birefringence sign (negative to positive) can lead to a 90-degree alteration in the local axis orientation because of the switch between the fast and slow optic axes. We then demonstrate, for the first time, that the local axis orientation can be utilized to map and visualize the WSLs from the healthy enamel with a unique contrast. Moreover, the sharp alte...
Various manipulations on JPEG images introduce single and multiple compression artifacts for forg... more Various manipulations on JPEG images introduce single and multiple compression artifacts for forged and unmodified areas respectively. Based on the statistical analysis of JPEG compression cycle and on the finite mixture paradigm, we propose in this paper a modeling framework for AC DCT coefficients of such tampered JPEG images. Its accuracy is numerically assessed using the Kullback-Leibler divergence on the basis of a tampered JPEG image dataset built from six well-known uncompressed color image databases. To illustrate the framework utility, an application in image forgery localization is proposed. By formulating the localization as a clustering problem, we use the plug-in Bayes rule combined with a simple EM algorithm to distinguish between forged and unmodified areas. Numerous experiments show that, when the quality factor of final JPEG compression is high enough, the proposed modeling framework yields higher localization performances in terms of F 1-score than prior art regardless of divers local manipulations. INDEX TERMS DCT coefficients analysis, EM algorithm, forgery localization, multiple JPEG compression, statistical image models, tampered JPEG images.
There remains a clinical need for an accurate and non-invasive imaging tool for intraoral evaluat... more There remains a clinical need for an accurate and non-invasive imaging tool for intraoral evaluation of dental conditions. Optical coherence tomography (OCT) is a potential candidate to meet this need, but the design of current OCT systems limits their utility in the intraoral examinations. The inclusion of light-induced autofluorescence (LIAF) can expedite the image collection process and provides a large field of view for viewing the condition of oral tissues. This study describes a novel LIAF-OCT system equipped with a handheld probe designed for intraoral examination of microstructural (via OCT) and microvascular information (via OCT angiography, OCTA). The handheld probe is optimized for use in clinical studies, maintaining the ability to detect and image changes in the condition of oral tissue (e.g., hard tissue damage, presence of dental restorations, plaque, and tooth stains). The real-time LIAF provides guidance for OCT imaging to achieve a field of view of approximately 6....
The formability of the drawn part in the deep drawing process depends not only on the material pr... more The formability of the drawn part in the deep drawing process depends not only on the material properties, but also on the equipment used, metal flow control and tool parameters. The most common defects can be the thickening, stretching and splitting. However, the optimization of tools including the die and punch parameters leads to a reduction of the defects and improves the quality of the products. In this paper, the formability of the camera cover by aluminum alloy A1050 in the deep drawing process was examined relating to the tool geometry parameters based on numerical and experimental analyses. The results showed that the thickness was the smallest and the stress was the highest at one of the bottom corners where the biaxial stretching was the predominant mode of deformation. The problems of the thickening at the flange area, the stretching at the side wall and the splitting at the bottom corners could be prevented when the tool parameters were optimized that related to the thi...
2018 IEEE International Symposium on Signal Processing and Information Technology (ISSPIT), 2018
Resampling is a common manipulation in creating tampered digital images. The goal of this paper i... more Resampling is a common manipulation in creating tampered digital images. The goal of this paper is to develop an efficient detector to distinguish between a resampled TIFF image from an original TIFF image. To this end, we first propose a statistical model for resampled TIFF images by analyzing the complete processing process from a RAW image to a resampled TIFF image. Next, we formulate the detection problem as a likelihood ratio test between the models of original and resampled TIFF images. The test power is analytically evaluated in the context that all model parameters of original TIFF images are unknown. Numerous numerical experiments justify the performances of the detector.
This paper report the development of non-invasive multi-functional imaging system for dental appl... more This paper report the development of non-invasive multi-functional imaging system for dental applications. This system is capable of detecting: 1) autofluorescence of the enamel, 2) red porphyrin of plaque, 3) the 3D-tomography of the hard/soft tissues and 4) functional angiography of said 3D-tomography data. The imaging technique incorporates molecular imaging (via light-induced autofluorescence, or LAF), 3D-high-resolution structure (via optical coherence tomography, or OCT) and angiography (via functional OCT, or OCTA) into one single imaging probe and platform. This development is crucial for our future research that would look into possible links between our OCTA findings and other clinical indicator such as red-porphyrin of plaque, autofluorescence of enamel.
While consensus exists regarding the association between organizational commitment and job satisf... more While consensus exists regarding the association between organizational commitment and job satisfaction, the temporal ordering of this association in proposed models frequently varies across empiri...
Gingivitis is highly prevalent in adults, and if left untreated, can progress to periodontitis. I... more Gingivitis is highly prevalent in adults, and if left untreated, can progress to periodontitis. In this article, we present an interesting case study where the resolution of gingivitis was followed over a period of 10 days using optical coherence tomography (OCT) and light‐induced autofluorescence (LIAF). We demonstrate that OCT and its functional angiography can distinctively capture the changes during the resolution of gingivitis; while LIAF can detect red‐fluorescent signals associated with mature plaque present at the inflamed site. The acute inflammatory region showed evidence of angiogenesis based on the quantification of vessel density and number; while no angiogenesis was detected within the less inflamed region. Gingival thickness showed a reduction of 140 ± 26 μm on average, measured between the peak gingivitis event and the period wherein the inflammation was resolved. Vessels in the angiogenesis site was found to reduce exponentially. The mildly inflamed site showed a decreasing trend in the vessel size, which however was within the error of the measurement.
The change in gingival tissue volume may be used to indicate changes in gingival inflammation, wh... more The change in gingival tissue volume may be used to indicate changes in gingival inflammation, which may be useful for the clinical assessment of gingival health. Properly quantifying gingival tissue volume requires a robust technique for accurate registration and segmentation of longitudinally captured 3-dimensional (3D) images. In this paper, a semi-automated registration and segmentation method for micrometer resolution measurement of gingival-tissue volume is proposed for 3D optical coherence tomography (OCT) imaging. For quantification, relative changes in gingiva tissue volume are measured based on changes in the gingiva surface height using the tooth surface as a reference. This report conducted repeatability tests on this method drawn from repeated scans in one patient, indicating an error of the point cloud registration method for oral OCT imaging is 63.08 ± 4.52µm (1σ), and the measurement error of the gingival tissue average thickness is -3.40 ± 21.85µm (1σ).
We report the development of an integrated multi-functional imaging system capable of providing a... more We report the development of an integrated multi-functional imaging system capable of providing anatomical (optical coherence tomography, OCT), functional (OCT angiography, OCTA) and molecular imaging (light-induced autofluorescence, LIAF) for in vivo dental applications. Blue excitation light (405 nm) was used for LIAF imaging, while the OCT was powered by a 1310 nm swept laser source. A red-green-blue (RGB) digital camera, with a 450nm cut-on broad-band optical filter, was used for LIAF detection. The exciting light source and camera were integrated directly with the OCT scanning probe. The integrated system used two non-invasive imaging modalities to improve the speed of in-vivo OCT data collection and to better target the regions of interest. The newly designed system maintained the ability to detect differences between healthy and hypo-mineralized teeth, identify dental biofilm and visualize the microvasculature of gingival tissue. The development of the integrated OCT-LIAF system provides an opportunity to conduct clinical studies more efficiently, examining changes in oral conditions over time.
We investigate the impact of stock market cycles on unlisted firms' investment activities. We... more We investigate the impact of stock market cycles on unlisted firms' investment activities. We find that bull markets is associated with increased capital expenditures, new establishments, and employment growth in the unlisted corporate sector, while bear markets is associated with a decrease in these investment activities. The favorable effect takes one year to materialize while the adverse effect takes place contemporaneously. Both effects are transitory and vanish after two years. The effects are stronger for unlisted firms with high capital requirements and facilitated in areas with a dense presence of listed firms. In addition, the magnitude of the effect is attenuated depending on the availability of alternative financing sources such as private equity and bank lending. We also find evidence suggesting stock market cycles partly impact the unlisted firm market through merger and acquisition activities by publicly listed firms.
This paper focuses on the digital image authentication and forgery localization using demosaicing... more This paper focuses on the digital image authentication and forgery localization using demosaicing artifacts. The aim is to build an algorithm allowing a bridge between the color filter array pattern and demosaicing algorithm estimation, and the statistical analysis of demosaicing artifacts in spatial domain to improve the authentication and localization performance. After analyzing the evolution of demosaicing traces in camera acquisition pipeline, a robust feature statistic characterizing demosaiced digital images is first developed on the basis of the noise residue of green channel. Such a feature statistic is less sensitive to the edges problem because only the smooth region of green channel is used in the development. Next, a single normal mixture model is proposed to describe the probability distribution of feature statistics for both original and tampered images. Therefore, normality tests can be used to authenticate automatically digital images. The authentication performance can be further improved by human interpretation of supported graphic tools. Finally, a penalized expectation-maximization algorithm is used to localize forged areas in tampered images. Numerous comparative studies on four well-known datasets show that the developed algorithm yields better performance and robustness than existing forensics algorithms of the same kind. INDEX TERMS Demosaicing traces, digital image authentication, forgery localization, normal mixture model, penalized expectation-maximization algorithm. NHAN LE received the Engineering degree in industrial engineering and management from the
Responding to calls for studies to examine the cross-level influence of team personality composit... more Responding to calls for studies to examine the cross-level influence of team personality composition, we hypothesized a crosslevel mediation model of the effects of different operationalizations of team conscientiousness (i.e., mean, minimum, maximum, and variance) on individual safety performance through team safety climate. We tested our model using a three-wave longitudinal design with a sample of 451 employees and 70 supervisors nested within 70 teams from two branches of one hospital. The results of our multilevel path analyses indicated that the mean, minimum, and variance-but not maximum-operationalizations of team conscientiousness at time 1 were significantly related to team safety climate at time 2. Further, team conscientiousness (i.e., mean, minimum, and variance) at time 1 exerted a top-down influence on both self-ratings and supervisor ratings of individual safety compliance and safety participation at time 3 through team safety climate at time 2, suggesting that team personality composition can influence outcomes at different levels of analyses. Theoretical and practical implications of these findings are discussed.
Quantitative imaging in medicine and surgery, 2017
Recent development of optical micro-angiography (OMAG) utilizes principal component analysis (PCA... more Recent development of optical micro-angiography (OMAG) utilizes principal component analysis (PCA), where linear-regression filter is employed to separate static and blood flow signals within optical coherence tomography (OCT). While PCA is relatively simple and computationally efficient, the technique is sensitive to and easily skewed by outliers. In this paper, robust PCA (RPCA) is thus introduced to tackle this issue in traditional PCA. We first provide brief theoretical background of PCA and RPCA in the context of OMAG where coherent (complex) OCT signals are utilized to contrast blood flow. We then compare PCA and RPCA on sets of 4D-OCT complex data (3 dimensions in space and 1 dimension in time), which are collected from microfluidic phantoms andnail-fold tissue. In phantom experiments, both analyses perform relatively well since there are little motion within our observation time window, albeit small tail-noise artifacts from PCA. In nail-fold experiment, PCA suffers from tis...
Elastography has the ability of quantitatively evaluating the mechanical properties of soft tissu... more Elastography has the ability of quantitatively evaluating the mechanical properties of soft tissue, thus is helpful for diagnosis and treatment monitoring for many diseases, e.g. skin diseases. Surface acoustic waves (SAWs) have been proven to be a non-invasive, non-destructive method for accurate characterization of tissue elastic properties. Current surface acoustic wave elastography using high energy laser pulse or mechanical shaker still have some problems. In order to improve SAW elastography in medical application, a new technique was proposed in this paper, which combines high intensity focused ultrasound (HIFU) as a SAWs impulse inducer and PhS-OCT as a SAWs detector. 2% agar-agar phantom and ex-vivo porcine skin were tested. The data were processed by a new algorithm based on the Fourier analysis. The results show that the proposed method has the capability of quantifying the elastic properties of soft tissue mimicking materials. The lateral resolution of the elastogram has...
Numerical simulation of high intensity focused ultrasound temperature distribution for transcrani... more Numerical simulation of high intensity focused ultrasound temperature distribution for transcranial brain therapy AIP Conference Proceedings 1816, 080007 (2017);
2016 3rd International Conference on Green Technology and Sustainable Development (GTSD), 2016
The camera cover is a complex 3D-part with many corners and is difficult to form in deep drawing ... more The camera cover is a complex 3D-part with many corners and is difficult to form in deep drawing process. One of the most common defects is the tearing that occurs at corners due to the tensile stress concentration. The suitable determination of die and punch parameters leads to reduce the defects and improve the quality of drawn part. Both numerical and experimental analysis can be useful to analyze the deep drawing process for determining the optimal values of tool parameters. In this paper, the formability of camera cover in deep drawing process was considered relating to the geometrical parameters of the die edge radius (RD), the pocket radius on bottom of die (RD1) and the punch nose radius (RP). The results showed that the thickening occurred in the flange area, the stretching occurred in the side wall and the tearing could be occurred in the corners above the punch nose that related to stress concentration if the tool parameters were not optimized. Also, the numerical and experimental results were a good agreement. Both numerical and experimental results cleared that the quality of camera cover relating the thickness was improved when the die geometric parameters were determined suitably with values of RD = 8 mm, RD1 = 4 mm and RP = 2 mm.
International journal of hyperthermia : the official journal of European Society for Hyperthermic Oncology, North American Hyperthermia Group, Sep 5, 2016
Phase-sensitive optical coherence tomography (PhS-OCT) is proposed, as a new high intensity focus... more Phase-sensitive optical coherence tomography (PhS-OCT) is proposed, as a new high intensity focused ultrasound (HIFU) imaging guidance to detect and track HIFU focus inside 1% agar samples in this work. The experiments studied the effect of varying HIFU power on the induction of shear wave, which can be implemented as a new technique to monitor focused ultrasound surgery (FUS). A miniature HIFU transducer (1.02 MHz, 20 mm aperture diameter, 15 mm radius of curvature) was produced in-house, pressure-field mapped, and calibrated. The transducer was then embedded inside a 1% agar phantom, which was placed under PhS-OCT for observation, under various HIFU power settings (acoustic power, and number of cycles per pulse). Shear wave was induced on the sample surface by HIFU and was captured in full under PhS-OCT. The lowest HIFU acoustic power output for the detection of shear wave was found to be 0.36 W (1.02 MHz, 100 cycles/pulse), or with the number of cycles/pulse as low as 20 (1.02 MH...
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Papers by Nhan Le